The heat-shock response of Streptococcus pyogenes following exposure to elevated growth temperatures, and the immunological reactivity of heat-shock proteins (HSPs) in streptococcal infections were studied. Two major proteins of 65 and 75 kDa were expressed when a S. pyogenes strain was shifted from 37 degrees C to heat-shock temperatures of 40, 42 and 45 degrees C. Such proteins are members of the GroEL and DnaK families recognised in a Western blot assay with polyclonal antibodies against Escherichia coli GroEL and E. coli DnaK, respectively. Two-dimensional autoradiograms of polypeptides labelled at 37 or 42 degrees C showed an increased intensity of three spots at 42 degrees C. A monoclonal antibody (MAb) against HSP 63 of Bordetella pertussis also recognised the 65-kDa inducible protein, although MAbs against Mycobacterium tuberculosis HSP 65 failed to recognise this protein. Immunoblot analysis of sera from individuals with rheumatic fever or uncomplicated streptococcal diseases revealed seven major immunogenic protein bands, two of which also reacted with anti-E. coli GroEL and DnaK polyclonal antibodies. Furthermore, antibodies to the GroEL and DnaK proteins were also detected in sera from patients with either rheumatoid arthritis or systemic lupus erythematosus. These results demonstrated a heat-shock response of S. pyogenes, and indicated the presence of an immune response against HSPs in streptococcal diseases.